1. Field of the Invention
The present invention relates to a valve for controlling a flow rate of fluid. More particularly, it relates to a flow control valve for controlling a flow rate of air sucked into an automobile engine.
2. Discussion of Background
There have been known flow control valves for an electronically controlled fuel injection type engine in which a by-pass passage is formed near a throttle valve in an air intake pipe to regulate a flow rate of air sucked into the engine by opening or closing the by-pass passage. For instance, a proportional type flow control valve is used to open and close the by-pass passage. There are several kinds of practically used proportion type flow control valves in which a linear solenoid or a stepper motor is used as a driving source. For the structure of the valve, there are classified a spool type, a poppet type and a rotary type. In this specification, description will be made as to a type of using a linear solenoid as a driving source.
FIG. 2 shows a cross-sectional view of a proportion type flow control valve which belongs the above mentioned linear solenoid type. In FIG. 2, reference numeral 1 designates a solenoid device in which a fixed iron core 2 is provided at the center of the inside of it in the longitudinal direction. A cylinder-like casing is disposed at the inner circumference of the solenoid device 1. A movable iron core 4 is disposed at a position facing the fixed iron core 2. A return spring 5 is interposed between the fixed iron core and the movable iron core 4.
The movable iron core 4 has a reduced diameter portion 4c, and a valve 14 is slidably fitted to the reduced diameter portion 4c. At the outer circumference of the reduced diameter portion 4c, a spring 15 is provided so as to urge the valve 14 in the front end side of it (on the left hand of the drawing). A holder 16 which restricts the movement of the valve 14 toward the front end side is fixed to the front end of the reduced diameter portion 4c. The valve 14 is relatively urged toward the movable iron core 4 by means of the spring 15 so that the valve 14 is brought to contact with the holder 16. Thus, a valve assembly 18 is constituted by the movable iron core 4, the valve 14, the spring 15 and the holder 16.
An electromagnetic coil 6 is disposed at the inner circumferential surface of the casing 3 through an insulating material 3a. A pipe 7 is disposed at the inner circumferential surface of a bobbin 6a on which the electromagnetic coil 6 is wound. The fixed iron core 2 and the movable iron core 4 are disposed facing each other inside the pipe 7. The above-mentioned return spring 5 is extended in the space between the fixed iron core 2 and the movable iron core 4 through a spring holder 5a, whereby the movable iron core 4 is pushed by the return spring 5 in the direction against an electromagnetic attractive force by the electromagnetic coil 6. Thus, the return spring 5 always exerts a force on the movable iron core 4 in the left-hand direction in FIG. 2. A lead wire 6b is connected to the electromagnetic coil 6.
A spring 8 is disposed at a position opposite the return spring 5 with respect to the movable iron core 4. The spring 8 is disposed between the spring holder 9 and the holder 16 which is fixed to the front end of the reduced diameter portion 4c of the movable iron core 4. The spring holder 9 is fixed to the front end of an adjusting screw 10 which is engaged with a proportion type flow control valve main body 11.
A fluid inlet passage 11a is formed in the vicinity of an end portion of the solenoid device side of the proportion type flow control valve main body 11. A fluid outlet passage 11c is formed at the opposite side (in the left end portion in FIG. 2) of the main body 11.
The proportion type flow control valve main body 11 is fitted to a ribbed guiding portion 19a formed in a guide member 19 which is in turn fitted to the end portion of the solenoid device 11 so that the solenoid device 1 and the proportion type flow control valve main body 11 are fixed to each other without looseness. The guide member 19 holds an end portion of the pipe 7 which supports the movable iron core 4 so as to be freely slidable. A valve seat 13 is fitted to the proportion type flow control valve main body 11 at a position facing the valve assembly 18, whereby a space 11b communicating with the fluid outlet passage 11c is separated from the fluid inlet passage 11a.
The adjusting screw 10 is engaged with the proportion type flow control valve main body 11 at a position near which the fluid outlet passage 11c is formed to extend toward the movable iron core 4. The spring 8, which is supported by the spring holder 9 fixed to the adjusting screw 10 always urges the movable iron core 4 in the same direction as the electromagnetic attractive force.
The valve assembly 18 receives the urging forces of the spring 8 and the return spring 5 so that the movable iron core 4 is brought to contact with the valve seat 13 in which there is a slight gap between the pipe 7 and the movable iron core 4 and there may occur a slight inclination of the movable iron core in the gap.
Since the spring 8 is disposed between the holder 16 and the spring holder 9, the spring force of the spring 8 can be adjusted by the adjusting screw 10 so that the urging force of the valve assembly 18 to the valve seat 13 can be adjusted. A contacting load by the valve 14 to the valve seat 13 is so determined that it is smaller than the contacting load between the valve 14 and the holder 16 by the spring 15 and there is no gap between the valve 14 and the holder 16 in an entirely closing state.
The contacting surface of the valve seat 13 is formed to have a tapered shape (a conical form). On the other hand, the contacting surface of the valve 14 is in a spherical form. The diameter of the circle formed by the contact of the contacting surface of the valve seat 13 to the contacting surface of the valve 14 is, for instance, 11 mm, the diameter being determined so as to be substantially agree with the inner diameter of the pipe 7 in which the movable iron core 4 is slidably moved.
The valve seat 13 and the valve 14 may be composed of polybutylene terephthalate (PBT).
A communicating hole 4b is formed in the axial center portion of the movable iron core 4 so that a pressure in the space 11b which communicates with the fluid outlet passage 11c is balanced with a pressure in a space formed between the movable iron core 4 and the fixed iron core 2. The diameter of the communicating hole 4b is determined to be 3 mm or more.
In the proportion type flow control valve having the construction described above, when an electric current is supplied to the electromagnetic coil 6, the movable iron core 4 is attracted to the fixed iron core 2 against the pushing force of the return spring 5, whereby the valve assembly 18 is moved to open the valve. In a case that the proportion type flow control valve is used to control a flow rate by using a duty control or a dither control, a repulsive force which takes place due to the separation of the valve from the valve seat owing to slight vibrations in the valve assembly 18 or a shock at the time of contacting the valve to the valve seat, which is derived from the duty control or the dither control, can be absorbed by the spring 15 which urges the valve 14.
In the above-mentioned case, the solenoid device 1 and the proportion type flow control valve body 11 are fitted to each other without looseness through the guide member 19, deviation of the contacting portions of the valve assembly 18 and the valve seat 13 takes place only by the inclination of the valve assembly 18, which is resulted from the gap between the outer circumference of the movable iron core 4 and the inner circumference of the pipe 7. Further, since the contacting surface of the valve seat 13 is in a tapered form and the contacting surface of the valve 14 is in a spherical form as described above, a circle having a predetermined diameter can be formed even though there is a slight inclination, whereby an excellent sealing function is assured. For instance, the gap of the pipe 7 and the movable iron core 4 which slides in the pipe 7 is in a range of 0.02 mm- 0.2 mm, and the ratio L/D of the length of sliding L to the diameter of sliding portion D is 1.5 or more.
Further, in the above-mentioned case, since the circle of contact of the valve 14 to the valve seat 13 substantially agrees with the sliding diameter between the movable iron core 4 and the pipe 7, the forces applied to the valve assembly 18 from the both sides are balanced by means of the communicating hole 4b even a negative pressure of the intake air pipe is applied to the fluid outlet passage 11c in a non-electric conductive state, whereby a stable condition can be maintained.
In a fluid control valve having a spool type valve or a rotary type valve, flow rate is controlled by controlling the surface area of air passage in the sliding portion. Accordingly, an amount of air leaking from the gap at the sliding portion can not be zero even when the valve is moved to the position at which the surface area of the air passage is entirely closed by turning-off the power source. The amount of leaking air can be reduced by minimizing the gap in the sliding portion. However, an allowable range of gap will be determined when it is considered that a smooth sliding movement has to be maintained and there may be deposition of oil or carbon and the scattering of the initial dimensions. Accordingly, although the spool type valve or the rotary type valve has an advantage that the flow rate can be changed in proportion to the stroke or an angle of rotation of the valve, they are disadvantageous in a case that the reduction of the amount of leaking air at the OFF time is considered to be most important.
In controlling a flow rate of by-passed air in an internal combustion engine, it is desirable to save fuel by reducing a flow rate of leaking air from the by-pass passage to zero to thereby reduce the revolution speed of the engine if it is unnecessary to flow the by-passed air in an idling state. In particular, since the absolute value of the flow rate of air necessary for the idling operation itself is small in a car having a small displacement, there is a possibility that the idling revolution of the engine can be maintained by only the flow rate of leaking air from the throttle valve side. In such case, it is preferably to improve the fuel consumption rate by reducing the flow rate of leaking air from the by-pass passage so as not to unnecessarily increase the idling speed of the engine.
Such improvement is most desirable in view of a relation of a grade of automobile to a fuel consumption rate.
From the reasons as described above, it is considered to be desirable to constitute a poppet type valve in order to reduce a flow rate of leaking air. In the proportion type flow control valve of this kinds including the pool type, the rotary type and the poppet type, there have been generally used a duty control wherein a current is supplied intermittently to the electromagnetic coil at a predetermined frequency and the ratio of an ON time and an OFF time is changed to thereby cause slight sliding movements of the movable iron core, or a dither control wherein variation (an Ac component) is given to a constant current value (a Dc component) to thereby cause slight sliding movements of the movable iron core, in order to reduce hysteresis due to a frictional resistance in the sliding movement section or to reduce hysteresis in the elastic repulsive force of the elastic member which is subjected to expanding and shrinking functions by the movable member.
Further, as methods for restricting the maximum flow rate of the valve, there have been used a method wherein the stroke of the movable iron core is mechanically controlled, a method wherein an attractive force and a spring force by the inner spring are balanced while the attractive force is saturated, and a method wherein an element to restrict the surface area of air passage is disposed in the flow rate controlling section. Generally, in consideration of reduction of an attractive force which is resulted by heat in the solenoid, the maximum flow rate is determined under the condition of about 80% of the maximum current.
In the above-mentioned conventional maximum flow rate controlling methods, there were disadvantages as follows. The method of mechanically controlling the stroke of the movable iron core had such disadvantages of occurrence of striking sounds and poor durability. The method of balancing the attractive force and the return spring force had such disadvantage that scattering of the maximum flow rate was unavoidable because of scattering of the attractive force, scattering of the load of the return spring and scattering of the valve position after assembling which is caused by the scattering of the dimensions of the structural elements. Further, the shapes of the structural elements which constitute a magnetic circuit have to be special in order to obtain such attractive characteristics, which pushed up manufacturing cost (Japanese Unexamined Patent Publication No. 88076/1990). Furthermore, in cases that a cylindrical portion 16a is formed in the holder 16 as shown in FIG. 3 and a structural element to control the surface area of passage such as a valve seat 13 having a cylindrical portion 13a is disposed in the flow control section as shown in FIG. 4, there may increase the number of structural elements to thereby increase manufacturing cost and decrease the processability in assembling the flow control valve.